Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the readOnlyHint annotation, the description adds valuable behavioral context: it returns the image itself plus the recipe, explains the coordinate conversion to prevent misplaced elements, and mentions existing screen contents to avoid duplication on a second pass. It also notes that proposals land in the owner's Inbox. No contradiction with the readOnlyHint annotation since the tool itself only reads/returns data.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is dense but well-structured. It is front-loaded with the 'SECONDARY (user-driven UI)' label and immediately states the action. Every sentence adds value: the return payload, coordinate conversion, duplicate prevention, the propose/update workflow, and the trigger condition. No filler or redundancy, though it is a bit long.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the absence of an output schema, the description does a good job explaining what the tool returns (image, recipe, canvas resolution, conversion, existing elements) and how to proceed (propose_element/update_element). It doesn't specify the exact recipe structure, but that is not essential for selecting the tool. It is sufficiently complete for a read-only tool with a clear trigger.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The 'screen' parameter is described in the schema as 'name or id', and the description elaborates on tracing that screen's reference image. However, 'project_id' has no description in the schema or the tool description (schema coverage is 50%), and the description does not compensate by explaining its role. The description adds some meaning via the recipe and conversion context but leaves project_id ambiguous.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's function: 'turn a screen's REFERENCE IMAGE into placed elements.' It uses specific terminology like 'recipe', 'fraction→pixel conversion', and distinguishes itself from siblings by emphasizing it is a 'SECONDARY (user-driven UI)' tool. This is a concrete verb+resource statement, not a tautology.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly states when to use it: 'Use when the user wants the wireframe to match a screenshot or mockup they uploaded.' It also labels the tool as 'SECONDARY (user-driven UI)' and instructs to follow up with propose_element/update_element, giving clear contextual guidance. It doesn't explicitly name alternatives or exclusions, but the trigger condition is sufficiently clear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.